Homogenizing method and apparatus



Dec 15, 1959 J. B. JONES ETAL 2,917,386

HOMOGENIZING METHOD AND APPARATUS Filed Sept. 9, 1955 Fig.

INVENTOR. I JAMES B. JONES ,9. 2 KENNETH H. YOCOM v MAW ATTORNEY2,917,386 HOMOGENIZING METHOD AND APPARATUS B. Jones and Kenneth H.Yocom, West Chester, Chester, Pa.,

James Pa., assignors to Aeroprojects, Inc., West a corporation ofPennsylvania Application September 9, 1955, Serial No. 533,279 13-Claims. (Cl. 99-63) The present invention relates to a method forforming stable homogenized mixtures, and more particularly, to a methodfor forming emulsions, suspensions, and colloidal mixtures. For example,the method of the present invention may be applied to the production ofemulsions consisting of a plurality of liquids which do not appreciablydissolve in each other, but in which one of the liquids is suspended inthe form of minute droplets in the other liquid; or a mixture of minutesolid particles suspended in a liquid; or colloidal mixtures consistingof a dispersed phase of minute solid or fluid particles surrounded by adispersion medium consisting of another fluid. The present invention isalso directed to apparatus for forming homogenized mixtures.

There are numerous emulsion, suspension and colloidal systems of greatcommercial importance, as for example dispersions of silver halideparticles in gelatin and water colloidal systems; various dairy productssuch as milk and cream; mixtures comprising oil and water;

beverages; paints and pigments; etc. A desirable attribute of each ofthe foregoing emulsion, suspension, and colloidal systems, is that suchsystems remain stable; namely that the dispersed phase must not separatefrom the dispersion medium, or tend to coagulate, or precipitate.

The formation of stable colloidal, suspension and emulsion systems byconventional means has frequently proved to be most costly anddifficult. Emulsions having great utility in which this problem ispresent are aqueous emulsions of gelatin and silver halide used as thephotosensitive medium in photographic films. With such emulsions thesilver halide should be evenly dispersed as minute suspended particlesin order that a photoemulsion of desirable properties may be obtained.Elaborate mechanisms and complex procedures have heretofore been adoptedfor breaking up or, preventing the formation of agglomerates of silverhalide in order to form stable photoemulsions.

Similar difficulties are encountered with the wetting of other solidparticles, such as barium sulfate, dried food particles, etc.

The problem is acute with certain paints, wherein the wetting of thepigment by the paint vehicle is effected only with great difliculty.

This invention has as an object the provision of a method whereby stablehomogeneous emulsions, or suspensions or colloidal systems may readilyand quickly be formed from substances which are substantially insolublein each other.

This invention has as a further object the provision of a method wherebyemulsions or suspensions are formed from agglomerates. I

This invention has as another object the provision of a method wherebyemulsions or colloidal solutions containing dispersed particles ofuniform and very small size may be obtained, and recovered.

This invention has as another object the provision of atent iceapparatus useful for homogenizing emulsions, colloids, suspensions andthe like.

The above and other objects are accomplished by the process of thepresent invention in which a mixture, such as a mixture of a solid and aliquid, or a mixture of mutually insoluble liquids is formed into astream. This stream is impinged upon a coaxially rapidly moving streamof a gas whose direction of movement is changed shortly after theimpingement, thereby effecting radial displacement of the liquid. Theradially displaced liquid is broken up into very minute particles and isthen collected on the surface of a surrounding collection vessel anddrained downwardly to yield a stable homogenized mixture.

The apparatus of the present invention comprises a shell having aplurality of inlets, such as inlets for gas and liquid which passthrough the shell into an aerosol generator disposed within the shell.By aerosol generator is meant a generator capable of generatingparticles having very small diameters, such as particles having a sizerange of the order of 60 microns in diameter, or smaller; preferably,below 10 microns. The shell is provided at its base with means forcollecting the homogenized product, and removing the same; and with avent, for removing the aerosolizing or propelling gas from the shell,which vent is provided with means for separating entrained particlesfrom the vented gas from the shell.

For the purpose of illustrating the invention there is shown in thedrawings a form which is presently preferred; it being understood,however, that this invention is not limited to the precise arrangementsand instrumentalities shown.

Referring to the drawings wherein like referencecharacters refer to likeparts:

Figure 1 is a schematic elevational view of an embodiment of apparatussuitable for practicing the method of the present invention.

Figure 2 is a longitudinal section through a nozzle useful for thepractice of the present invention.

Referring to the drawings and initially to Figure 1, wherein anembodiment of apparatus suitable for the practice of the presentinvention is shown, the mixture to be homogenized is introduced into theapparatus through line 10. In the specific embodiment of the presentinvention here-illustrated, such mixture comprises a mixture to be usedas a photoemulsion, namely 3 weight percent of gelatin and 10 weightpercent of a silver halide, such as silver bromide, dispersed indistilled water.

It has been found by microscopic examination of superior photoemulsions,that such photoemulsions comprise minute particles of the silver bromideindividually coated by the colloidal gelatin, which occupies theinterstices between the individual grains of silver bromide.

While the process of the present invention is illustrated for thepreparation of photoemulsions, it is, of course, to be understood thatthe process of the present invention is applicable to the homogenizationof other suspensions, emulsions, and/or colloids, or the stabilizationof such mixtures, as for example the stabilization of dairy productssuch as milkand cream containing milk fats, water and oil dispersions,paints, pigments, etc.

The slurry mixture is fed through line 10 to generator 12, which isdisposed within a substantially closed vessel 14, spaced beneath theceiling 16 thereof. The free edge of vessel 14 is received on anelastomeric or like base 18, such as synthetic rubber or like, whoseouter edge has been rabbetted to provide a tight seal with the freeedge. Base 18 is provided with a drain 20 having a valve 22 disposedtherein through which the homogenized product 38 may be removed fromvessel 14.

The mixture from line 10 enters the generator head designated 24,passing therein from line through channel 26 and thence through annularopening 28.

The propellent gas is introduced through line 30. The propellent gasshould be an inert gas, where as in the subject example, interreactionbetween the mixture in line 10 and the propellent gas is undesirable. Inthe subject example, a satisfactory propellent gas to be introducedthrough line 30 is air at room temperature. The propellent gas namelyair, is pressurized to above about 1.5 atmospheres, preferably above 1.7atmospheres and moves from line 30 through line 32 and issues fromgenerator head 24 through outlet 34 at supersonic or nearly supersonicvelocity, drawing the slurry mixture from concentric. annular opening 28into a sleeve-like envelope about it.

The rapidly moving gas stream carrying the envelope of liquid isimpinged onto barrier 36. Impingement of the gas stream drasticallydistorts the gas stream from a unidirectional or axially moving streaminto a substantially radial or disk-like pattern which radiatesoutwardly.

The sleeve-like liquid mixture surrounding the gas stream undergoesenormous blending forces upon distortion of the gas stream, resulting inan intimate degree of mixing of the mixture components, and subdividingof such mixture components into minute discrete particles ofsubstantially uniform size suspended in the liquid (e.g. the silverbromide particles are broken into minute grains suspended in the gelatinand water colloidal system). Simultaneously the liquid mixture isdispersed onto the surrounding wall of vessel 14 as fine droplets havingaerosol dimensions.

The generator 12, described in the present embodiment is the excellentaerosol generator disclosed in the co-pending application for UnitedStates Letters Patent Serial No. 441,039, filed July 2, 1954, entitledApparatus and Method for Generating Aerosols, in the name of James B.Jones. While this form of generator is to be preferred, other forms ofaerosol generators capable of generating an appreciable percentage offine droplets within the aerosol size range and preferably within thesize range of droplets having diameters of 10 microns or less may besubstituted for generator 12.

The fine droplets of the homogenized mixture are collected on the wallof the vessel 14 in the form of a film. This film moves downwardly alongthe inner surface of the wall of vessel 14 and collects in a pool 38 atthe base thereof.

The vessel 14 is provided with a vent 40 in ceiling 16 for removing thepressurized propellent gas. Vent 40 includes an angular conduitterminating in a single orifice discharge nozzle 42. A barrier 44consisting of a metal plate having a face juxtaposed to discharge nozzle42, is spaced from discharge nozzle 42, and deflects any dropletsissuing therefrom into entrapment vessel 46 which is provided with acollector outlet shown diagrammatically at 48 through which collectedhomogenized material may be removed. The vented gas is removed fromentrapment vessel 46 through vent opening 50, which may be provided withan additional deflector roof or barrier 52 for deflecting any entrainedliquid carried thereby onto the outside of vessel 46. Such deflectedliquid may be conveyed along the outer surface of collector outlet 48,and retained in the same receiver into which collector outlet 48 isdischarging.

A separator vessel 46, or other separating or coagulating means such asa filter or an electrostatic precipitator, such as a Cottrellprecipitator, must be utilized in the apparatus of the present inventionbecause we have found that aerosol droplets, particularly those dropletshaving diameters of 10 microns or less will tend to become entrainedwith the rapidly moving propellent gas, even to passing around a cornerwith such gas, so that a significant portion of such droplets may belost unless the auxiliary separating means, namely entrapment vessel 46is provided.

In fact, in some cases, particularly where a high percentage of thegenerated droplets have very small diameters, it may be advisable toemploy a plurality of entrapment vessels in series to avoid loss ofmaterial through entrainment with the propellent gas.

Under the aforesaid operating conditions homogenization of the sprayedmaterial into a stable photoemulsion having a uniformly distributeddispersion of fine grains of silver bromide coated with gelatin may beachieved.

The present invention may be embodied in other specific forms withoutdeparting from the spirit or essential attributes thereof and,accordingly, reference should be made to the appended claims, ratherthan to the foregoing specification as indicating the scope of theinvention.

We claim:

1. A method for homogenizing a mixture of a plurality of generallymutually insoluble materials including a liquid medium, which methodcomprises contacting a rapidly moving stream of gas with a coaxiallyenveloping stream of such mixture, impinging the rapidly moving streamof gas upon a barrier and deflecting it at an angle to its normaldirection of movement, said deflection of the gas stream effecting anintimate degree of mixing between the components of the mixture andsimultaneously breaking the mixture into aerosol droplets andsubdividing the materials carried by the liquid medium into minutediscrete particles uniformly distributed within the liquid medium,capturing said droplets upon a surface, and collecting said captureddroplets to form a pool.

2. A method in accordance with claim 1 in which the mixture includessolid particles.

3. A method in accordance with claim 1 in which the mixture consists ofa plurality of liquids which are substantially insoluble in each other.

4. A method in accordance with claim 1 in which the gas stream is movingat a supersonic velocity.

5. A method in accordance with claim 1 in which the mixture comprises anaqueous gelatinous medium and particles of a silver halide.

6. A method in accordance with claim 1 in which the mixture comprises anaqueous mixture of milk fats.

7. A method in accordance with claim 1 in which the mixture comprises awater and oil dispersion.

8. A method in accordance with claim 1 in which the mixture comprises amixture of pigment materials and a vehicle therefor.

9. A method in accordance with claim 1 in which the surface of one ofthe materials of the mixture is thoroughly wetted by the liquid mediumcomponent.

10. A method for homogenizing a mixture of a plurality of generallymutually insoluble materials including a liquid medium, which methodcomprises contacting a rapidly moving stream of gas with a coaxiallyenveloping stream of such mixture, impinging the rapidly moving streamof gas upon a barrier and deflecting it at an angle to its normaldirection of movement, said deflection of the gas stream effecting anintimate degree of mixing between the components of the mixture andsimultaneously breaking the mixture into aerosol droplets andsubdividing the materials carried by the liquid medium into minutediscrete particles uniformly distributed within the liquid medium,capturing a portion of said droplets upon a surface, collecting saidcaptured droplets to form a pool, entraining the remainder of thedroplets in a gas stream, capturing entrained droplets from said gasstream upon a surface, and collecting said last-mentioned captureddroplets.

11. A method for homogenizing a mixture of a plu- 'rality of generallymutually insoluble materials including a liquid medium, which methodcomprises contacting a rapidly moving stream of gas with a coaxiallyenveloping stream of such mixture, impinging the rapidly moving streamof gas upon a barrier and deflecting it at an angle to its normaldirection of movement, said deflection of the gas stream efiecting anintimate degree of mixing between the components of the mixture andsimultaneously breaking the mixture into aerosol droplets andsubdividing the materials carried by the liquid medium into minutediscrete particles uniformly distributed within the liquid medium,capturing a portion of said droplets from the gas stream upon a surface,collecting said captured portion of the droplets to form a pool,removing the gas stream and the remainder of the droplets from theregion of the barrier, capturing entrained droplets from the remainderof the droplets carried by the removed gas stream upon a surface, andcollecting said last-mentioned captured droplets in a pool.

12. A method in accordance with claim 11 in which the captured entraineddroplets from the remainder of the droplets carried by the gas stream isformed into a pool which is discrete from the pool formed from thefirst-captured droplets.

13. In homogenizing apparatus for continuously producing a homogeneousmixture of a plurality of generally mutually insoluble materialscomprising a liquid, the improvement which comprises a generally closedvessel, a propellant gas inlet extending through the wall of said vesselinto the interior thereof, a separate liquid inlet extending through thewall of said vessel into the interior thereof, an aerosol generatordisposed within said vessel and spaced from the walls of said vessel,said aerosol generator comprising a plurality of concentric conduits,the innermost conduit being in communication with the propellant gasinlet, and an outer conduit being in communication with the liquidinlet, a barrier juxtaposed to and spaced from the discharge orifices ofsaid conduits, the discharge orrifice of said innermost conduit being atleast as close to the juxtaposed face of said barrier as the dischargeorifice of said outer conduit, means for collecting homogenized productat the base of said vessel, means in communication with the base of saidvessel for withdrawing homogenized product from said vessel, and ventingmeans for removing gas from said vessel, said venting means includingmeans for separating and collecting entrained liquid aerosol dropletsfrom said vented gas.

References Cited in the file of this patent UNITED STATES PATENTS1,152,456 Vogelsang Sept. 7, 1915 1,839,193 Blanchard Jan. 5, 19321,878,052 Wilson et al. Sept. 20, 1932 2,069,455 Massa Feb. 2, 19372,284,023 Scripture May 26, 1942 2,323,877 Turbett July 6, 19432,597,422 Wood May 20, 1952 2,605,088 Dautrebande July 29, 19522,709,577 Pohndorf et a1. May 31, 1955

1. A METHOD FOR HOMOGENIZING A MIXTURE OF A PLURALITY OF GENERALLYMUTUALLY INSOLUBLE MATERIAL INCLUDING A LIQUID MEDIUM, WHICH METHODCOMPRISES CONTACTING A RAPIDLY MOVING STREAM OF GAS WITH A COAXIALLYENVELPING STREAM OF SUCH MIXTURE, IMPINGING THE RAPIDLY MOVING STREAM OFGAS UPON A BARRLIER AND DEFLECTING IT AT AN ANGLE TO ITS NORMALDIRECTION OF MOVEMENT, SAID DEFLECTION OF THE GAS STREAM EFFECTING ANINTIMATE DEGREE OF MIXING BETWEEN THE COMPONENTS OF THE MIXTURE ANDSIMULTANEOUSLY BREAKING THE MIXTURE INTO AEROSOL DROPLETS ANDSUBDIVIDING THE MATERIAL CARRIED BY THE LIQUID MEDIUM INTO